Currently, there are several WLAN interworking schemes with 3GPP systems (UMTS). In one scheme, the end to end tunnel approach, the UE establishes a tunnel with the 3GPP based system ending at a Packet Data Gateway (PDG). The tunnel goes through a WLAN Gateway (WAG) without being terminated at the WAG (and is transparent to the WAG). This scheme has been standardized as a preferred configuration that all I-WLAN UEs must implement.
The second scheme is the switched tunneling approach, which involves establishing two tunnels between the PDG and the UE at the WAG. The first tunnel between the WAG and the PDG uses existing 3GPP based general packet radio service (GPRS) tunneling protocol (GTP) and the second tunnel follows the normal IP tunneling protocol.
A third interworking scheme is the Generic Access approach, which involves the tunneling of the traffic from the 3GPP system to the 3GPP-based UE via the I-WLAN. In this scheme, the I-WLAN acts as a pseudo 3GPP Node B interworking with the 3GPP system at the radio access network (RAN) level. The traffic passes through the I-WLAN access point (AP) to the I-WLAN UE which decodes the traffic back to 3GPP formats and passes it to the 3GPP-based terminal.
The existence of these schemes creates potential conflicts regarding the preferred mode of operation. For example: 1) the UE is capable of supporting all of the configurations, but does not know what configuration is supported by the network; 2) the UE is only capable of supporting one scheme (for example, the end to end tunneling architecture), but the network is configured to use another interworking scheme (for example, the switched tunneling solution); 3) the UE and the network are capable of supporting all schemes, but currently there is no way to communicate the preferred mode of operation between the two sides.
These schemes are different in terms of operational protocols and parameters. The end result is that multiple techniques or schemes may be used to support I-WLAN interworking with 3GPP systems (cellular in general), which mandates that the UE should either support all of these schemes or some mechanism to decide which scheme is being supported at the infrastructure level and then configures the UE to operate in accordance with the supported scheme. During the set-up, there should be procedures to inform the UE of the network configuration, such that it uses the right interworking protocol.